I'm new here too, but this is my understanding of kbin: Lemmy is like the fediverse reddit. Mastodon is like the fediverse twitter. There's a fediverse facebook alternative (can't remember the name). Image hosts, video hosts etc.
kbin talks them all and can be your central hub. Imagine facebook, reddit and twitter etc all merged their websites. But you have a single fediverse identity.
Yeah, as others have mentioned, kbin ≠ Lemmy, but because of the magic of the fediverse, they talk to each other. But I like kbin better since it also interoperates with Mastodon, Calckey, etc as well. Easier than Lemmy at any rate.